Daniel L. Everett arrives in the Amazon intending to learn the Pirahã language and translate the New Testament. He faces severe environmental hazards during his early fieldwork. His scientific observations of Pirahã communication methods cause him to question his assumptions about linguistics. As he spends more time in the jungle, his worldview shifts away from his evangelical training.

Keren Everett is a dedicated missionary who grew up in the Amazon as the child of missionaries. She possesses cultural fluency that aids her family's long-term residence in the jungle. During their early years she suffers a near-fatal bout of malaria requiring a harrowing emergency evacuation. She manages the household and actively collaborates on linguistic data gathering.

Noam Chomsky is an influential American linguist who revolutionized his field by proposing the theory of universal grammar. He posits that humans are born with an innate grammatical structure. He specifically points to recursion as a uniquely human language component. He represents the deductive academic establishment that Everett's fieldwork challenges.

Kóhoibiíihíai is a Pirahã man who serves as Everett's principal language teacher. He patiently instructs the linguist in the unique phonemes of his native tongue. He acts as a cultural liaison by demonstrating the community's reliance on immediate experience. He occasionally challenges Everett's assumptions about authority and intervention.

Shannon is Daniel and Keren's eldest daughter. She contracts a severe case of malaria early in their stay, forcing an emergency evacuation downriver to seek medical attention. Following her recovery she adapts to jungle life and forms close friendships with Pirahã children.

Kristene is one of Daniel and Keren's daughters who grows up partially in the Amazon. She learns to see the beauty in a culture that initially feels alien to her. She adapts seamlessly to the environment alongside her siblings.

Caleb is the youngest child of Daniel and Keren. He travels with his father and sister Kristene to Porto Velho during the chaotic medical evacuation of his mother and older sister. He spends his formative years surrounded by the Pirahã community.

Arlo Heinrichs is a missionary-linguist from the Summer Institute of Linguistics who preceded Everett in the Amazon. He produced the first phonemic analyses for the Pirahã language. His foundational linguistic work provides an essential starting point for Everett's research.

Steve Sheldon is a missionary who documented Amazonian languages prior to Everett's arrival. He produced systematic analyses of Pirahã grammar and recorded traditional stories. His previous presence establishes continuity that benefits subsequent researchers.

Túkaaga is a Pirahã teenager from the village of Coatá. Influenced by river traders, he leads an ambush against a neighboring Apurinã man to protect Pirahã territory. His violent actions bring the threat of outside police intervention to his people.

Joaquim is an Apurinã man living near the Pirahã at the settlement of Ponto Sete. He considers himself materially superior to the Pirahã people though he believes they maintain friendly relations. He becomes the victim of a violent territorial dispute when local traders manipulate teenagers into attacking his family.

Godofredo Monteiro is a caboclo river trader who assists the Everett family during their emergency medical evacuation. He becomes a friend to Everett, demonstrating the practical and stubborn values of caboclo culture. He firmly relies on traditional beliefs over modern medicine for his own family.

Levinho is a FUNAI anthropologist working to formally map and demarcate Pirahã territory. Initially resentful of having to rely on an American translator, he comes to appreciate Everett's skills. He becomes fascinated by the Pirahã culture's lack of creation myths.

Xará is a senior representative of the Brazilian government's Indigenous agency. He is dedicated to guaranteeing that isolated groups can maintain their traditional ways of life. He organizes the expedition to officially demarcate reservation boundaries.

Darciel Colário is a river trader involved in a bitter feud over access to jungle products. He arms Pirahã teenagers in an attempt to forcefully remove his competitors from the territory.

Tomé is an Apurinã man who survives a violent attack organized by local traders. He is forced to relocate downriver following the territorial dispute.

Paitá is the son of Everett's primary language teacher. His brief interactions with his father provide Everett with critical linguistic data regarding how the Pirahã structure their sentences without using recursion.

Juarez is the son of a local caboclo river trader. He operates within the traditional caboclo economic system where children are viewed as necessary assets for family labor.

Ronaldinho is a racist river trader who attempts to sell illegal alcohol to the Pirahã. He exploits the villagers and nearly instigates a violent attack on the Everett family before facing direct confrontation.